A common problem with conventional type snow throwers is that the chute through which the snow is discharged can become obstructed with compacted plugs of snow and ice. This compaction typically occurs throughout the snow discharge chute. It thus becomes necessary for the operator to clean out the movable portion of the chute, and to displace the snow and ice in the lower stationary portion of of the chute into the impeller area so that it will e discharged upon subsequent operation of the thrower. Operators, sometimes employ their hands or a stick to clean out the directional movable portion and to dislodge the snow in the lower stationary portion of the chute. If the impeller blades are turning and the stick or hand comes into contact with them, injury to the operator can result. Recognizing this tendency of operator behavior, and knowing that an operator will not want to stop and restart the motor to accomplish this cleaning, snow thrower manufacturers have equipped their machines with clutches so that the impeller blades may be temporarily disengaged from the rotational energy supplied by the motor. The impeller blades will, however, continue to turn idly due to their rotational inertia. This creates a very dangerous situation as the operator may begin to clean out the discharge chute under a mistaken belief that because the clutch has been disengaged there is not rotation of the impeller blades.
Prior devices, as disclosed in U.S. Pat. Nos. 3,497,263 and 4,761,901, have attempted to prevent injuries to the operator by placing guards to prevent the insertion of the operator's hand into the discharge chute. These obstructions however also impede the flow of ice and snow through the discharge chute thus contributing to the accumulation problem. These guards also prevent the operator form clearing the discharge chute. for these reasons, operators will frequently remove these devices, thus negating their safety function.
In an attempt to safely dislodge accumulated ice and snow from the discharge chute, one device, as disclosed in U.S. Pat. No. 3,921,315, employs a spring loaded "M" shaped element pivotally mounted in the chute, and several prongs which extend from the movable portion into the stationary portion. The "M" shaped element prevents insertion of the operator's hand and upon rotation of the movable potion, the prongs presumably scrape any accumulated ice and snow from the inner surfaces of the stationary portion. This device si ineffective in a number of snow throwers. The "M" shaped element suffers from the same drawbacks described above as of the guards, and the prongs are not adapted to dislodge any accumulations blocking the movable portion. In addition any hindrance to the free rotation of the movable portion renders ineffective the prongs as a method for dislodging snow and ice. Such a hindrance may come about from corrosion occurring and/or ice collecting in the relief between the movable portion and stationary portion. Finally, the structure of the plug may be such that the portion of the lug in the movable portion may support the portion of the plug in the stationary portion and the scraping of the prongs around the circumference of the stationary portion may not cause the plug in the stationary portion to dislodge.